Brake-induced fork judder on cyclocross bike

penexpers

edit: moved from here

blorg wrote: »

Looks good. Any thoughts on the CR520 brakes so far?

blorg

penexpers wrote: »

Looks good. Any thoughts on the CR520 brakes so far?

They are CR720s thank you very much :mad:

Basically the same as the CR520 I believe but with cartridge pads. They are probably a bit better than low-profile cantis I have used before but they have that typical canti feel and stopping power is pretty bad to be honest. Substantially worse than mini-Vs. If you jam the front brake on the bike just slows until it gets down to a low speed at which point crazy fork judder starts. I've had that before with cantis/Vs but this is worse than I've ever seen. In fairness it is controllable, it only happens when I have been absolutely jamming the brakes on to test stopping distances.

I had been thinking of changing my tourer over to wide-profile cantis but based on this I don't think that I will. Pads are close enough to the rim too so not even much of an advantage there, about the one thing they would have over Mini-Vs for this application would be better mud clearance.

Lumen

blorg wrote: »

If you jam the front brake on the bike just slows until it gets down to a low speed at which point crazy fork judder starts. I've had that before with cantis/Vs but this is worse than I've ever seen.

Have you read this/this?

(sorry for continuing off-topic)

blorg

Lumen wrote: »

Have you read this/this?

(sorry for continuing off-topic)

I haven't yet, no, although I have read a few other bits about fork judder which is a common enough occurrence with cantis/Vs... To be honest the fork judder is not a major problem, it only occurs with the brakes jammed on at very low speeds, doesn't happen at the start of braking at high speed. It is a super lightweight cross fork, one of the lightest available in mainstream production I believe. This no doubt contributes. But the bigger issue is that the brakes just don't stop the bike the same way calipers or Vs do.

@Lumen- Maybe split out this bit of the thread from Penexpers' post to the main forum?

Lumen

Blorg,

FWIW, I have recently installed TRP EuroX cantis (as recommended by dave2pvd and billy.fish).

They have a similar straddle wire design as yours, but I've set them up a bit lower, so that the straddle wire junction is level with the fork crown or whatever it's called. Haven't measured the angles yet, but the braking is very powerful, although a little squeaky since I haven't toed in yet. A whole load better than the woeful stock Deore cantis anyway - I have both better clearance and more power.

I have another pair on order for the rear.

Those articles are worth reading, IMO...

penexpers

Lumen wrote: »

Blorg,

FWIW, I have recently installed TRP EuroX cantis (as recommended by dave2pvd and billy.fish).

They have a similar straddle wire design as yours, but I've set them up a bit lower, so that the straddle wire junction is level with the fork crown or whatever it's called. Haven't measured the angles yet, but the braking is very powerful, although a little squeaky since I haven't toed in yet. A whole load better than the woeful stock Deore cantis anyway - I have both better clearance and more power.

I have another pair on order for the rear.

Those articles are worth reading, IMO...

Yeah they make for interesting reading.

My current setup is Tektro RX-5 mini-V's with some Tektro levers and some Cane Creek interrupters. Braking is powerful enought and while I manage to stop, it's very grabby and there's practically no modulation.

Interesting to see that Zinn eventually went with Cane Creek drop levers.

One option that I am currently consdering is Eurox on the front with the RX-5 on the back.

blorg

I think I'll try lowering them, see if that helps matters. dave2pvd seems to indicate in that post that the CR720s can be made to work anyway.

blorg

penexpers wrote: »

Yeah they make for interesting reading.

My current setup is Tektro RX-5 mini-V's with some Tektro levers and some Cane Creek interrupters. Braking is powerful enought and while I manage to stop, it's very grabby and there's practically no modulation.

Interesting to see that Zinn eventually went with Cane Creek drop levers.

One option that I am currently consdering is Eurox on the front with the RX-5 on the back.

For what it's worth you can run normal Vs with the Tektro RL520 levers and the braking is very good- I have this set up on my fixed Tricross. I have the Tektro R200 levers on my Bowery (with calipers) and don't think the levers are quite as good but still work a lot better than on the cross bike.

It only gets messy I think when you want both STI levers and wide tyre clearances, with non-STI levers you can just get a better brake lever for the application.

billy.fish

What Lumen said, EuroX all the way

Check the article Zinn wrote last week on CX brakes and shudder its worth the read

blorg

Honestly, as I said the shudder is not a problem. It's the lack of stopping power compared to calipers or Vs.

ROK ON

Hi. Some advice reqd. I recently put cane creek Vs for a bike after previous brakes (tektro cantis) died on me.
The rear break now has fantastic stopping power. The front brake however has appalling stopping power andhuge screeching noise whilst braking.
Apologies for off topic but it is a cross bike.
How do I stop the screeching anx improve the braking.

Lumen

ROK ON wrote: »

The front brake however has appalling stopping power and huge screeching noise whilst braking.

Don't know much about V brakes, but screeching is generally a (lack of) toe-in issue.

blorg

OK, I lowered the front brake straddle bridge and stopping power is much improved. To the extent that judder is now serious on hard braking! So I will have to look at toeing in etc. It's a strange sort of sensation though, I can actually skid the front wheel (on tarmac- without crashing too) but don't get the over the handlebars effect at all. On my road bike I would be going up over the bars before I would get a skid. Maybe thats the bike geometry? Road is a bit wet right now though too.

@ROK_ON- are they Vs or mini-Vs and what sort of levers are you using with them? You need mini-Vs if using STI levers, or otherwise a travel agent. V brakes have fixed mechanical advantage so if you are using the right brakes with the right levers I could only imagine it is differing cable tension between front and rear. You might also want to check the centering- this is done with the little bolts/screws on either arm. Screw them in to move the brake away from the rim, screw them out to move the brake towards the rim.

As to the squealing, this is common and Sheldon has a few tips, as Lumen suggests toe-in can help. I get it to an extent on most of my bikes with cantis or Vs and to be honest it doesn't bother me so much, as Sheldon suggests it does not really compromise the braking power I see it as somewhat like a form of bell. It's only where there is severe juddering with the squeal that it becomes a problem.

mayan

I've got some 720's on my Jake the Snake, messed about a little with the straddle height etc and toe in, which has fixed the (minimal) squealing and juddering I first had with them.
But, the biggest difference to actual braking power I made was to change the cartridge pads to Kool Stop dual compound (kinda pinky and black). This make a massive difference, and I can easily lock both wheels from the drops.
(Im running Ultegra STI's, Kona carbon cyclocross fork and the straddle cable is quite low, so the angle of at the top is greater than 90 degrees)

billy.fish

blorg wrote: »

Honestly, as I said the shudder is not a problem. It's the lack of stopping power compared to calipers or Vs.

Cross brakes will stop faster than a set of V's in 90% of conditions.

You just need to set them right.

Stradle cable height, bridge to cable height, and arm angle are all important. IT takes a while and allot of cursing

blorg

Thanks for the suggestions. I have some Kool Stop all-salmon pads already that would fit these, think 720s take V-Brake pads anyway? @Mayan- do you think the dual compound are better than the all-salmon?

@Billy.fish- yes there was a lot of cursing I can assure you! What do you think of the angle I have now, should it be lower still for a wider angle at the top? I think I have it around 90 now. Braking is certainly better but not what I'd call spectacular. I also have the pads so close to the rim I can't release the brakes to get the wheel out other than by undoing the bolt.

mayan

Ive never used the all salmon ones, just the stock pads that came with the tektros and the stock pads that came with the shimano BR550's on my pomino. I replaced both withe dual compound kool stops and it made a world of difference.

I would try moving the stradle cable down a little as well. The angle of mine is def shallower / greater than 90 deg. Probably sits maybe 1 inch above the tyre, but i guess thats specific to the fork / tyre combo.

blorg

Went up to the top of Three Rock at lunch where I bumped into Ryan Sherlock. Coming back down my rear wheel punctured. Cause of the puncture was interesting, it was a nick just at the bottom of the valve. Turns out the previous owner of my back wheel seems to have mounted the tube with the valve nut on the INSIDE of the tyre, and it ended up pinching a hole.

I then got lost and ended up going down a trail very unsuitable for a cross bike but that's another story.

mudrock

blorg wrote: »

think 720s take V-Brake pads anyway?

The earlier link to Zinn's article about brake shudder says that longer pads make the problem worse. According to sheldon brown, the lower you drop the straddle cable, the higher the mechanical advantage. You drop it too much, you can't release the QR on the cable, as you found out. I'm getting a Tektro RX5 mini v-brake for my cross bike to get rid of my shudder - should also give me more leverage. With Campy levers (and integral QR on the levers) it should work great.

cdaly_

blorg wrote:

mounted the tube with the valve nut on the INSIDE of the tyre

This was suggested to me by an LBS after I showed them the valve ripped out of tube due (maybe) to me overtightening the nut on the outside...

Maybe best thing is to leave off the nut altogether.

mudrock

Putting the valve nut on the inside of the rim is nuts (pardon the pun) - I would question any shop that suggests that. If users keep tearing valves off at the base by pumping their tires, the answer is to be gentler. One could try a washer on the inside with the nut on the outside. Bend a curve in the washer to match the curvature of the rim. Better yet - go tubeless with Hutchinsons.

blorg

mudrock wrote: »

The earlier link to Zinn's article about brake shudder says that longer pads make the problem worse. According to sheldon brown, the lower you drop the straddle cable, the higher the mechanical advantage. You drop it too much, you can't release the QR on the cable, as you found out. I'm getting a Tektro RX5 mini v-brake for my cross bike to get rid of my shudder - should also give me more leverage. With Campy levers (and integral QR on the levers) it should work great.

I have Tektro RX5 brakes on my tourer. They provide VERY good braking power indeed and with excellent modulation, far better than I have ever managed from cantis. Very easy setup too. Have normal V brakes on my Tricross, with V-brake specific non-STI levers, they are also excellent. No significant shudder either. However with STIs and the RX5s you do need to run them VERY close to the rim so any buckle at all and you really are fecked. This happened to me touring in Sicily and I bascially had to release the rear brake entirely, there was no way to stop it rubbing and have the brake still work at all. But it is looking like I have to run the cantis very close too so not sure it is so much of an advantage.

Have you got the Tektros yet? I have a pair that I would sell if not.

cdaly_ wrote: »

This was suggested to me by an LBS after I showed them the valve ripped out of tube due (maybe) to me overtightening the nut on the outside...

Maybe best thing is to leave off the nut altogether.

Well putting it on the inside caused a pinch hole just at the base of the valve. It was Lumen's wheel, I suspect it was a ploy to hobble me in Sunday's race. It's not necessary to use the nut at all, indeed many tubes come without them entirely.

Lumen

blorg wrote: »

Well putting it on the inside caused a pinch hole just at the base of the valve. It was Lumen's wheel, I suspect it was a ploy to hobble me in Sunday's race. It's not necessary to use the nut at all, indeed many tubes come without them entirely.

LOL. No idea how that happened. It wouldn't be a favoured technique of mine (the inside nut that is, although cheating and sabotage is definitely my style).

As I recall, the wheels didn't match anyway - one of them came from my Tricross. I think DualFrontDiscs has the reverse non-matching set.

edit: I find using those nuts (on the outside) helps get the track pump hose on. Maybe my technique is wrong. I know Skeff doesn't bother.

blorg

Lumen wrote: »

As I recall, the wheels didn't match anyway - one of them came from my Tricross. I think DualFrontDiscs has the reverse non-matching set.

We did a swap so he now has the Tricross wheels and I have the matching Concept wheels.

mudrock

blorg wrote: »

Have you got the Tektros yet? I have a pair that I would sell if not.

Thanks for the offer, but I live in the States - wouldn't be worth it. I can get the RX5s here for only 17USD, don't know how that equates to the Euro (does Ireland use the Euro?) I use Campy brifters, which my local shop tells me pulls a bit more cable than STI. And I still have a usable QR after installing the v-brake, so I hope to avoid your problem.

blorg

mudrock wrote: »

Thanks for the offer, but I live in the States - wouldn't be worth it. I can get the RX5s here for only 17USD, don't know how that equates to the Euro (does Ireland use the Euro?) I use Campy brifters, which my local shop tells me pulls a bit more cable than STI. And I still have a usable QR after installing the v-brake, so I hope to avoid your problem.

We are Euro, yes. The Mini-Vs work very very well indeed, the only issue is how close you need to set them to the rim in my experience. They can trivially throw you over the bars while having reasonable modulation.

billy.fish

Main prob with Mini-v's is going to be mud clearance.

If you are going to race, not worth it, if for general pottering about. GO for it

blorg

billy.fish wrote: »

Main prob with Mini-v's is going to be mud clearance.

If you are going to race, not worth it, if for general pottering about. GO for it

Mud clearance on the pads or over the top? I have wide cantis on my cross bike, have never used the Mini-Vs in the mud. Mini-Vs do work well on the road if you want wide tyres.

billy.fish

blorg wrote: »

Mud clearance on the pads or over the top? I have wide cantis on my cross bike, have never used the Mini-Vs in the mud. Mini-Vs do work well on the road if you want wide tyres.

Top, side, pad to rim, everywhere!

penexpers

I got a set of CR720's (just for the front) to try them out. Set them up today, very easy to install. From the stand, they seem to be very powerful compared to the old mini-v's. Going to test them outside when it stops snowing. If they are ok, I will order a set for the rear too.

blorg

penexpers wrote: »

I got a set of CR720's (just for the front) to try them out. Set them up today, very easy to install. From the stand, they seem to be very powerful compared to the old mini-v's. Going to test them outside when it stops snowing. If they are ok, I will order a set for the rear too.

The way cantis feel on the stand has NO bearing whatsoever on how they perform on the road. Sheldon touches on this but I know it myself from bitter experience. They feel nice and sharp on the stand but you can jam them on on the road and the bike just slows.

Let me know how you get on but if you aren't using STIs I would just get V-specific brake levers, as I mentioned I have these on my Tricross fixed along with standard Vs and it has by far the best braking of any of my wide clearance bikes. The only real reason for all the fudging is that STIs have inadequate cable pull to work with standard Vs (plus mud clearance in cross but that's not an issue on road.)

Sheldon Brown wrote:

"Feel" vs. Function
With automobile brakes, a nice "hard" pedal feel is a sign that the brakes are in good condition. A soft, "spongy" feel at the brake pedal is a sign of trouble, perhaps air in the hydraulic lines. This is not the case with bicycle brakes. A hard, crisp feel to the brakes on a bicycle may be a sign that the brakes don't have much mechanical advantage. You squeeze them until the brake shoes hit the rim, then they stop. Brakes with a high mechanical advantage will feel "spongy" by comparison, because the large amount of force they deliver to the brake shoes will squash the shoes against the rim, deforming them temporarily under pressure. You can feel this deformation in your fingers. The brakes with the rock-hard feel may seem nice on the work stand or the showroom floor, but when it comes to making the bike actually stop, the spongy set-up will do the job better, with less finger pressure and greater margin for safety in wet conditions.

penexpers

blorg wrote: »

The way cantis feel on the stand has NO bearing whatsoever on how they perform on the road. Sheldon touches on this but I know it myself from bitter experience. They feel nice and sharp on the stand but you can jam them on on the road and the bike just slows.

Hah yeah I found that out too. Have them closer to the rim now and they are great. Excellent stopping power though I would like some more modulation I think (I could move them back from the rim some more though).

Let me know how you get on but if you aren't using STIs I would just get V-specific brake levers, as I mentioned I have these on my Tricross fixed along with standard Vs and it has by far the best braking of any of my wide clearance bikes. The only real reason for all the fudging is that STIs have inadequate cable pull to work with standard Vs (plus mud clearance in cross but that's not an issue on road.)

I am using some Tektro drop levers (same ones as you have) and I have Cane Creek interrupters.